The present invention relates to a sizing composition for paper making, and more particularly to an internal sizing composition having an excellent self-emulsifying property suitable for use in neutral paper making.
Hitherto, as a sizing agent for use in paper making, there have been broadly used various sizing agents, for example, sizing agents prepared from natural rosin or denatured rosin and the like, and particularly fortified rosin sizing agents prepared by saponifying the addition reaction product of rosin and maleic acid.
These sizing agents are employed in acid sizing method in which they are fixed to paper fibers by aluminum sulphate. However, the acid sizing method has a number of drawbacks that devices or machines employed in paper making are corroded and that strength and durability of the obtained paper deteriorates because of pH drop in pulp slurry due to employment of aluminium sulphate which is an essential component in paper making by the acid sizing method.
Also, there is little hope that the cost of paper making is lowered largely because cheap alkaline fillers such as calcium carbonate are difficult to use in the acid sizing method.
For the purpose of eliminating such drawbacks of the acid sizing method, a neutral paper making method in which aluminium sulfate is not employed was studied and there have been proposed neutral sizing agents capable of imparting an excellent sizing effect to a paper under a papr making condition in neutral region. Examples of such a neutral sizing agent are, for instance, a sizing agent containing cyclic dicarboxylic acid anhydride described in Japanese Examined Patent Publication (Tokkyo Kokoku) No. 2305/1964, a sizing agent prepared by addition reaction of an olefin having a double bond at its inner part and maleic anhydride described in Japanese Examined Patent Publication No. 28526/1978 and a sizing agent consisting of substituted dicarboxylic acid anhydride, polyoxyalkylene compound and water described in Japanese Examined Patent Publication No. 36044/1978 and the like.
However, both sizing agents described in Japanese Examined Patent Publications No. 2305/1964 and No. 28526/1978 have many limitations in order to disperse the dicarboxylic acid ayhydride in water as clearly understood from the description in Japanese Examined Patent Publication No. 36044/1978. They can be dispersed in water only when protective colloids which are emulsifiers such as cationic starch, gelatine and polyvinylalcohol are added, and a special device for violent agitation such as high-speed vibrator, mechanical homogenizer or ultrasonic wave homogenizer is used.
There is described in Japanese Examined Patent Publication No. 36044/1978 that the emulsifying process employing such a violent agitator can be omitted by using polyoxyalkylene compound as a surfactant in combination with the substituted dicarboxylic acid anhydride. Thus, in case of dispersing the substituted dicarboxylic acid anhydride in water with usage of a surfactant described in Japanese Examined Patent Publication No. 36044/1978 such as polyoxyalkylene alkyl ether or polyoxyalkylene alkylaryl ether, emulsification can be achieved only by passing the admixture containing the substituted dicarboxylic acid anhydride through a pulp-mixing aspirator or orifices without agitating violently.
However, admixture of the substituted dicarboxylic acid anhydride and the above-mentioned surfactant has a tendency to lower its dispersibility in water as passage of time and thus, a tendency of lowering its sizing effect.
Also, when polyoxyalkylene alkyl diester is used as a surfactant as described in Japanese Examined Patent Publication No. 36044/1978, an admixture containing the diester does not have such a drawback of lowering sizing effect with passage of time as an admixture in which polyoxyalkylene alkyl ether or polyoxyalkylene alkyl aryl ether is added. But, polyoxyalkylene alkyl diester has another drawback that the ester is not easily dispersed in water by normal mixing operation because the ester has many carbon atoms in its alkyl group and thus, is a strong hydrophobicity.
Therefore, as easily understood from the above description, any dispersing agent disclosed in the above Publications cannot be used preferably.
The well-known neutral sizing agents cannot simultaneously satisfy the dispersibility in water, the storage stability and the sizing effect.
Consequently, an acid paper making method employing the fortified rosin sizing agent is still mainly conducted.
The object of the present invention is to provide a neutral sizing composition suitable for use in paper making which solves the above-mentioned problems and can be employed preferably in practical use comparing favorably with the fortified rosin sizing agent.